Milk of magnesia or magnesium hydroxide applied in a freshly precipitated form has been found to be an effective deodorant. The milk of magnesia can be evenly applied by a pump spray bottle as a slurry based on a mixture of alcohol and water. It has also been found that a mixture of the hydroxides of zinc and magnesium can provide long lasting protection against odor due to perspiration particularly with a mole excess of magnesia. These materials are active ingredients, and as such can be applied in a variety of ways such as aerosols, moisturizing creams, sticks, sprays and roll-on type applicators with the usual type of scents, softeners, moisturizers and emollients as desired.
The materials of this invention, not previously identified as deodorant agents, provide active hydroxide, in a manner compatible with good skin care, to neutralize 3-methyl-2-hexanoic acid and similar materials that have been demonstrated to be largely responsible for body odor associated with perspiration. These weak organic acids are produced by a bacterial action and require a moderately strong hydroxide type base to neutralize them and eliminate odor associated with, but not confined to perspiration.
Numerous agents have been used to combat perspiration and perspiration odor. As pointed out in U.S. Pat. No. 3,996,346 a range of acidic to neutral to basic salts have been proposed as active ingredients to reduce body odor and/or stem perspiration. Many of the salts cited in the patent can be injurious to the skin. Acid salts such as aluminum chloride, for example, hydrolyze to form hydrochloric acid, which can be injurious to both skin and clothing. Additionally, aluminum has been identified as a potential contributor to Alzheimer Disease. Potassium alum has become widely available, and while effective as a deodorant, it hydrolyzes to form even more injurious sulphuric acid as well as aluminum in a soluble ionic form, which can lead to higher rates of absorption into the body than is the case with aluminum metal or alumina.
These salts have hydrolysis points or protolysis reactions because they hydrolyze at different points on the pH scale (Chemistry of the Elements, Greenwood and Earnshaw, 1984) and precipitate out of solution, primarily as hydroxides, at various pH's. For example, ferric hydroxide precipitates or hydrolyzes out of solution a pH of about 2.6 to 4.0 while aluminum hydroxide precipitates or hydrolyzes out of solution in the range of 3.6 to 4.2.
Other salts, such as zinc, precipitate as hydroxides in the range of 6.5 to 8.0, but salts of these materials can behave in an erratic manner with many individuals in that they work effectively for very irregular periods of time. In addition, zinc sulphate still releases sulphuric acid upon hydrolysis. The sporadic efficacy may be due to lack of hydrolysis, conversion to relatively inactive carbonate or oxide, or some combination of these factors.
Basic materials have been proposed, such as in U.S. Pat. No. 74,871; U.S. Pat. No. 1,558,406; U.S. Pat. No. 2,114,559; and U.S. Pat. No. 2,187,163. There are problems with most of these materials.
The carbonates of U.S. Pat. No. 74,871 are very soluble and quickly leach from the skin during perspiration. Some agents are very basic and could be injurious to the skin.
The active agent of U.S. Pat. No. 1,558,406, a hexametaphosphate, is soluble and liable to be washed away during perspiration. Being a phosphate, this agent could well serve as a major nutrient source of the bacteria believed to be responsible for body odor and this agent could thereby promote body odor rather than diminish it.
U.S. Pat. No. 1,558,405 contains mention of some of the same basic materials mentioned in U.S. Pat. No. 74,781 and includes "sodium bicarbonate, potassium bicarbonate, sodium or potassium carbonate, calcium hydroxide and the like . . . ". The term "and the like" is vague, nebulous, undefined and unspecified given the previous explicit identification of agents. Materials mentioned, such as potassium carbonate and lime, are very basic and could injure skin and clothing. This patent claims that basic agents need to be combined with "an absorptive insoluble filler material of emollient character, such as the stearate of zinc, aluminum or magnesium, or a mixture of talc and small portions of zinc oxide". The basic materials were said to lead to a drying action, which is offset by the healing action of the emollient. The patent does not prescribe deodorant formulations consistent with current understanding of mitigation of body odor due to perspiration.
While bases in high concentration may have "drying action", they primarily neutralize acids as is evident to those skilled in the art. The only "anti-acid" body listed in the claims, which if compatible with the body, is sodium bicarbonate. It is not capable of neutralizing the agents responsible for body odor.
The patent does not teach that if the formulations had any significant efficacy, it did not arise from the action of the basic agent, sodium bicarbonate, cited in the claim but from some other material or combination of materials. Metal stearates, the so-called "absorptive insoluble filler material of an emollient character" of the formulation, might, under some circumstances, be responsible for some, if any, activity associated with the formulation cited in this patent. Another possibility is zinc oxide, but it along with many other "basic" metal oxides like alumina are very unreactive against perspiration odor due to insolubility and low hydrolysis rate to a hydroxide form that could show some activity.
The filler materials are first and foremost sparingly soluble neutral metallic salts of a weak organic acid which would only be weakly hydrolyzed to a potentially active agent with the aluminum salt having the best potential for any efficacy due to its low hydrolysis pH.
The zinc salts would show some erratic behavior as noted before but would be strongly inhibited by being coupled to a weakly dissociated organic acid. The magnesium salt would be no more effective than Epsom salts since it has no capacity of generate basic deodorizing agent through dissolution in water.
The zinc stearate cited as the emollient could have some antiperspirant activity but is likely subject to the erratic activity noted earlier for zinc salts. The stearate portion could supply organic material to foster undesirable bacterial growth and therefore be undesirable.
U.S. Pat. No. 2,187,163 identifies the use of "base" carrier materials such as kaolin or calamine with the latter being preferred when combined with active deodorant materials such as aluminum and zinc chloride. Calamine, zinc oxide and sulphates of aluminum and zinc are claimed as active agents. It is said that these formulations supplanted with other agents such as tannic acid and/or salicylic acid "have the property of preventing or reducing perspiration and of acting as deodorants in this manner".
Oxides and carbonates of "acceptable" antiperspirant agents, such as alumina and calamine, are generally ineffective in reducing body odor because they are inactive with respect to the weak organic acid responsible for perspiration odor for reasons of equilibrium, kinetics and solubility. Sulphates of zinc, unlike those of aluminum, have been observed to be erratic performers likely because they do not hydrolyze effectively. The author claims that the sulphates of aluminum and zinc have the property of reducing or preventing perspiration and act as deodorants in this manner.
There is no evidence in the text to support this assertion and it is evident to those skilled in the art that neither compound would act to any significant extent as a desiccant. These agents most likely act in a different manner and understanding of the mechanism of this action could result in a significantly different approach in formulating materials with greater efficacy.
Body odor is known to those skilled in the art to be due primarily to the products of bacterial action and not moisture as such.
U.S. Pat. No. 3,996,346 cites zinc oxide and calcium hydroxide along with phenol as an effective deodorant. As is evident by the citation of U.S. Pat. No. 1,558,405, the use of lime as deodorant agent has been noted some time ago. Given the low activity of zinc oxide as a deodorant agent, it is likely that any observed deodorant activity is due to the lime. Lime is quite basic with reported pH's of 12.5 and higher. While lime has the capability to function as an effective agent against odor, it is less desirable than other agents due to its alkalinity. The zinc oxide combined with stearic acid as a cream base most likely is an attempt to minimize the undesirable effects due to high alkalinity and the general undesirable nature of phenyls in skin care products.
In summary, there is a wide range of active ingredients cited in the open and patent literature for prevention of body odor and perspiration but most have some undesirable characteristics. Many formulations use aluminum chloride or other aluminum compounds based on sulphates for example that form irritating acids. As well, human exposure to aluminum is raising health concerns. Other formulations recommend materials, such as potassium carbonate, that can be harmful to the skin, or salts of zinc that have minimal efficacy due to poor hydrolysis to active hydroxide.
There is, therefore, a need to bring forward alternative deodorant formulations that balance the need for performance, efficacy, simplicity, and compatibility of the formulation with good health care in conjunction with a technically sound understanding of the reason for body odor and therefore the correct abatement measures to take.